1. Field of the Invention
This invention provides a chemical preservative for cereal grains, rendered animal by-products, silage, and complete animal feeds to prevent deterioration by fungus and bacteria and the formation of mycotoxins by the combined use of a n-butyric acid salt and a propionic acid salt.
1. Discussion of the Background
It is common practice to use fungicides in animal feedstuffs. The typical fungicide contains propionic acid or its sodium, calcium or ammonium salt in some form. Some commercial products are granular materials consisting of liquid propionic acid dispersed on a carrier. Others include aqueous solutions of propionic acid and aqueous solutions of ammonium propionate. Attempts have been made to improve the antifungal activity of propionic acid and its salts by combining them with a second volatile fatty acid and in some cases an improvement was observed although usually the results were disappointing. For instance, in 1973 the U.S. Grain Marketing Research Center of the U.S. Department of Agriculture at Manhattan, Kansas, issued a report entitled "Grain Preservatives for High-Moisture Feed Grain" by Dr. David Sauer. It was found that propionic acid alone was far superior to mixtures of propionic:formic, propionic:acetic, and propionic:isobutyric in all ratios tested.
Huitson et al, U.S. Pat. No. 3,595,665 disclosed a method for preventing mold growth in crops and animal feedstuffs during storage based on binary and ternary mixtures of lower carboxylic acids. In this case, it appeared that acetic/propionic acid and formic/acetic/propionic acid mixtures were more effective than the individual acids. Mixtures containing propionic acid and n-butyric acid or isobutyric acid were not investigated.
Herting et al, Cereal Chem. 51:382-388 (1974) reported that isobutyric acid is the most effective antifungal agent among the common C.sub.1 -C.sub.4 acids and that mixtures such as propionic:n-butyric:water (25:25:50) and propionic:isobutyric:water (25:25:50) are more effective than the individual acids in water. It was found that activity depended on the amount of water in the mixture; surprisingly, the activity increased as the proportion of water was increased. However, the presence or absence of mold was determined visually which is too imprecise method to draw valid conclusions.
Skov et al, U.S. Pat. No. 4,183,953 added isobutyric acid to aqueous ammonium isobutyrate in order to lower the crystallization temperature from 32.degree. F. to about -20.degree. to -40.degree. F., thus enabling the use of ammonium isobutyrate solutions in unheated areas in cold weather. The relative antifungal activities of ammonium isobutyrate alone vs. isobutyric acid/ammonium isobutyrate were not reported. We have tested similar mixtures of propionic acid and ammonium propionate, at different ratios and pH values, and found no improvement in biological activity.
It is known that n-butyric acid, like isobutyric acid, is an effective fungicide. However, it smells even worse than isobutyric acid and has not been used commercially. Many salts of n-butyric acid are less malodorous than the free acid, but are still highly objectionable to users and to the livestock who must eat the treated feed. Therefore, neither n-butyric acid nor its salts have been considered to have any practical utility as an animal feed preservative. We have discovered that n-butyric acid and its salts exhibit a strongly synergistic microbial-inhibiting effect in combination with salts of propionic acid. Further, we observed that n-butyrate/propionate mixtures are significantly more effective than isobutyrate/propionate mixtures. Therefore, the effective quantity of n-butyrate mixtures can be reduced to the point where the presence of n-butyric acid and its salts is no longer objectionable. This effect provides true utility for n-butyric acid in the field of animal feedstuffs for the first time, and represents one of the few commercial applications available for this material considering its terrible smell.